When manufacturing wooden articles, such as ice lollies and chopsticks, it is essential to remove defective articles no matter whether the defect is due to the stick being lopsided, having knots, having the wrong dimensions or being discolored.
The object of the present invention is to provide an apparatus which at a great speed, corresponding to the speed of manufacture of the article in question, can perform an effective control so that the approved manufactured goods are usable and appear uniform and preferably comely.
According to the invention the apparatus of the above stated type is characterised by the control devices comprising at least one first set of optical fibers situated opposite to each other on each side of the conveyor and at a predetermined height whereby the optical fibers on one side are adapted to emit a light ray along and parallel with the surface of the article, and whereby the optical fibers on the other side are adapted to receive the emitted light ray. The latter fibers are connected to a light sensitive detector adapted to provide a signal to a microprocessor. At least a second set of optical fibers is placed at mutually different heights close to the upper edge of a reflective plate member being elevationally slidable in response to the thickness (height) of the article. The optical fibers are adapted to emit and receive an optionally reflected light ray. The mutual, elevational location of said optical fiber is arranged so that an article being too high causes a reflection of more than a predetermined number of the second set of optical fibers, and an article being too low causes a reflection of less than a predetermined number of the light-rays emitted from the second set of optical fibers. The optical fibers of the second set of optical fibres are connected to light sensitive detectors adapted to receive the reflected light rays and depending thereon to provide signals to the microprocessor. One or more screen scanning camera(s) are mounted so that the conveyor and a number of articles thereon can be scanned from above and/or from below. The control device further includes devices for activating the screen scanning camera in response to the speed of the conveyor and preferably each time an article passes. The screen scanning camera is adapted to provide electric signals, representing one or more pictures of the scanned area. The picture signals are transferred to the microprocessor, which is adapted to process and evaluate the picture signals in order to determine width, curvature in the horizontal plane and length of each article and to compare these quantities with predetermined values, and based on this comparison, the microprocessor whether or not the article is to be discarded and provides corresponding impulses to the grading device.
In this way an unusually fast and effective grading of the articles is achieved. The first set of optical fibres grades articles curving in the perpendicular plane as such curvatures cause the article to block a light ray which can only pass if the article is linear and not too thick. The second set of optical fibres grades articles which are to high or too low, and such second set of optical fibres is preferably placed on each side of the conveyor so that both ends of the article are measured. By means of the camera and the associated microprocessor all dimensions in the horizontal plane can be controlled. By means of the suggested apparatus a very fast control in all three dimensions of a spatial article is achieved. The apparatus is particularly suitable for flat, oblong articles, such as ice lollies and chopsticks.
The width is preferably determined locally at intervals along the article. The article is preferably divided into a number of transverse sections and an average width for each section can be determined. The curvature is preferably measured in the horizontal plane as an aberration from a predetermined straight line. By the described apparatus it is possible to control the color of the article. According to the invention, the microprocessor is adapted to determine the total color level of the article by summing up the light intensity over the entire article.
Local color variations can advantageously be determined by summing up the light intensity in a number of limited areas and determining optional variations.
Small local areas having a particularly low light intensity are preferably registered. In this way it is possible to ascertain whether or not the article is knotty. According to the invention, predetermined acceptable values can be recorded in the microprocessor in order to compare the same with the data achieved by control of the articles. Such data are preferably recorded in the microprocessor during a learning phase by sending a number of first-grading-articles through the apparatus, which then measures and registers the characteristics of the articles. Such learning-articles are to be selected so that they only fulfil the desired margins defined by these articles to the microprocessor. Preferably the apparatus is adapted to receive an alternative set of margin-values corresponding to a second-grading of the articles.